Abstract—Low-level wind can be used to represent winter monsoon as an index constructed from 850 hPa wind. The vector empirical orthogonal function (VEOF) method is used to decompose variability of the low-level wind from JRA-25 reanalysis data during the boreal winter (December to February) over the Indochina peninsular. The first VEOF mode exhibits tropical anomalous easterlies over the southern region and anomalous southeasterlies over the central of region. A spatial pattern in positive phase of the first mode exhibits anomalous northeasterlies, and the pattern of negative phase reveals anomalous southwesterlies over the interior of the region. The variability of winter monsoon over the Indochina peninsular shows interannual variation, and long term variability is of interest. The relationship of winter monsoon over the Indochina peninsular to the East Asian winter monsoon (EAWM), which is a major climate feature during boreal winter, is investigated and discussed.

Index Terms—Indochina peninsular, variability, vector empirical orthogonal function, winter monsoon.

S. Sooktawee is with the Joint Graduate School of Energy and Environment, King Mongkut's University of Technology Thonburi, Bangkok 10140, Thailand, on leave from Environmental Research and Training Centre, Department of Environmental Quality Promotion, Ministryof Natural Resources, Pathum Thani 12120, Thailand (e-mail: sooktawee@jgsee.kmutt.ac.th).
U. Humphries is with Department of Mathematics, King Mongkut's University of Technology Thonburi, Bangkok 10140, Thailand. (e-mail: usa.wan@kmutt.ac.th).
A. Limsakul is with the Environmental Research and Training Centre, Department of Environmental Quality Promotion, Ministry of Natural Resources, Pathum Thani 12120, Thailand (e-mail: atsamon@deqp.go.th).
P. Wongwises is with the Joint Graduate School of Energy and Environment, King Mongkut's University of Technology Thonburi, Bangkok 10140, Thailand. (e-mail: prungchan.won@kmutt.ac.th).

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Cite: Sirapong Sooktawee, Usa Humphries, Atsamon Limsakul, and Prungchan Wongwises, "Low-Level Wind Variability over the Indochina Peninsular during Boreal Winter," International Journal of Environmental Science and Development vol. 3, no. 2, pp. 130-135, 2012.